This invention relates to an electric motor-activated clutch mechanism for an electronically controlled automatic transmission, and more particularly to a control method for operating the motor.
While hydraulic controls have traditionally been used to control the torque capacity of an automatic transmission clutch mechanism, the trend is to use electro-hydraulic or electromechanical controls in order to reduce the size and cost of the transmission and to provide increased control flexibility. In a particularly advantageous approach, an electric motor can be used to control the clutch torque capacity by coupling the motor to the clutch through a torque-to-thrust converter such as a ball-ramp or roller-ramp mechanism. In this case, the clutch torque capacity is controlled by controlling the angular position of the motor output shaft.
However, the performance requirements for the control can be difficult to achieve with conventional open-loop or closed-loop control strategies due to variations in the frictional and inertial characteristics of the torque-to-thrust converter. Accordingly, what is needed is a simple, high performance, motor control method for a motor-activated clutch mechanism.
The present invention is directed to an improved motor position control method for a motor-activated clutch mechanism including a torque-to-thrust converter, where the control utilizes a model-based feed-forward control in combination with a closed-loop position feed-back control. The desired clutch torque capacity is characterized in terms of a desired motor position, and the feed-forward control models the motor speed and position response to changes in the desired motor position. The modeled speed and position, in turn, are used to create a feed-forward command, and the feed-forward command is combined with a feedback command based on actual position error.